Liquid crystal display (LCD) panels are typically illuminated via backlight systems. Such backlight systems may comprise a light source and a diffuser for distributing light from the light source at a substantially constant luminance (e.g., brightness) over a range of viewing angles. Typically, backlight systems used to illuminate LCD panels distribute light in a fixed output pattern to the LCD panel. The output light pattern may differ for differing backlight system configurations. For example, the light distribution pattern may be optimized for on-axis viewing (e.g., viewing from a substantially normal direction to the LCD panel) by using a narrower angular distribution. Alternatively, for off-axis viewing (e.g., viewing from a direction at an angle, either vertical or horizontal, to the normal axis of the LCD panel) a wider angular distribution may be used.
Conventional backlight systems do not, however, permit selective variation (e.g., selective modulation) of the output light distribution pattern. In other words, conventional backlight systems are not tunable in the sense that the output light pattern may be altered as desired (e.g., selectively altered by a user). As such, when one type of viewing is desired, the LCD panel may be provided with a first filtering mechanism, such as an overlay screen. However, when a different light distribution pattern is desired, then a completely different filtering mechanism configuration is required.
In many applications, including, for example, aeronautical and combat settings, it may be desirable to control the illumination of a display element, such as, an LCD panel, and allow viewing of the display element over a range of viewing angles (both narrow and wide). By way of example, in some circumstances it may be desirable that an image from a LCD panel be viewed only by a single viewer or viewers (e.g., a pilot, military personnel, etc) sitting at a particular angle relative to the LCD panel, for example, substantially in alignment with the normal axis to the LCD panel. In other circumstances, it may be desirable that an image from a LCD panel be viewed by viewers that are positioned across a wide angle of view relative to the normal axis of the LCD panel. For the former situation, it may therefore be desirable to provide an output light pattern that is substantially focused in a relatively narrow angular range for on-axis viewing, while for the latter situation, it may be desirable to provide a wider angle distribution of the output light pattern.
In order to permit the light from an LCD panel or other light source to be substantially focused to a relatively narrow range of angles or to be distributed over a wider range of viewing angles, it may be desirable to permit an output light distribution pattern to be selectively modulated. For example, it may be desirable to permit a user of an LCD panel to selectively vary the distribution pattern of light transmitted from the LCD panel to vary from a relatively narrow angular range of distribution to a relatively wider angular range of distribution. For example, it may be desirable to permit the output light pattern of a backlight system to vary from a strong on-axis illumination distribution pattern to a substantially isotropic distribution pattern. It may also be desirable to permit variation of the output light pattern without having to remove and/or replace filtering mechanisms associated with an LCD panel or other display element or light source.
Further, it may be desirable to provide a light distribution device configured for selective variation of an output light distribution pattern for use with other applications in which it may be desirable to vary the light distribution pattern, including an angular light distribution pattern. It also may be desirable to provide a light distribution device configured for automated selective variation of an output light distribution pattern.